Don't Guess - Soil Test - March 2014

I’m Leo Espinoza, a state soil specialist with the University of Arkansas System Division
of Agriculture. I’d like to talk to you about soil testing today. [Slide – This is
a presentation of the Arkansas Soybean Podcast. Soil Testing with Leo Espinoza. For
more information on soil testing go to our website at www.uaex.edu. Slide – Picture of Leo Espinoza, Associate Professor and Soil Scientist, Crop, Soil
and Environmental Science University of Arkansas System Division of Agriculture. Ph.D.
in Soil and Water Science (Soil Chemistry – Water Quality), University of Florida,
1997.]

The numbers in your soil test report represent an estimate of the amount of plant-available
nutrients in your soil. [Video shows a field. Dr. Espinoza sitting at his desk discussing
soil testing.] The concentration of nutrients -- for instance potassium -- not only
vary across a field, but it can also be very dependent on weather conditions. Within
a field, potassium levels can vary due to changes in topography, texture or drench.
One needs to keep in mind that these conditions don’t hold true for every field in
Arkansas. As cultural practices are major drivers in the variability we observe within
a field. [Slides showing spatial mapping of a field indicating spatial variability
of potassium in a field. Picture of a field with cracks in the soil.]

Potassium levels can also be affected by weather conditions. For instance, on the
extended dry conditions, potassium levels will tend to be lower than normal. So we
may have soils that will show higher amounts of potassium, and we may have some other
soils that will show lower amounts of potassium than normal. [Video shows fields
with dry soil conditions. Slide shows temporal variability chart of soil K concentration
between 2010-2013 in Marianna, AR.]

Keep in mind that soil test levels typically do not change dramatically from year
to year. Particularly if the soil test levels are medium to optimum.

So how do we know if a particular soil test result is accurate or not? Here is the
real value of soil testing comes into play. [Slide – Chart showing soil structure
nutrient concentrations do not dramatically change between 2006-2014 season.] The
real value of soil testing is not on the ability of running one sample, or the value
associated with just one sample. The real value is on the ability of developing a
history of nutrient levels for a particular field for as long as a farmer has worked
such field. If a farmer has a soil test for say the last 10 years, he can easily see
whether or not a particular soil test result is way off of his historical average.
[Video shows a field.]

Keep in mind also that the 10 percent variability of soil test result is probably
is considered normal. So don’t guess, soil test. Thank you. [Slide – Don’t Guess,
Soil Test. Your Arkansas Soybean Podcast is a production of the University of Arkansas
System Division of Agriculture Cooperative Extension Service. University of Arkansas
Division of Agriculture Research and Extension University of Arkansas System. Arkansas
Soybean Promotion Board. For more information on soybean farming in Arkansas visit
www.uaex.edu.]